Heating requirement and its costs in greenhouse structures: A case study for Mediterranean region of Turkey Murad Canakci a,n , N. Yasemin Emekli b,1 , Sefai Bilgin a,2 , Nuri Caglayan a,3 a Akdeniz University, Faculty of Agriculture, Department of Agricultural Machinery, 07070 Antalya, Turkey b Akdeniz University, Faculty of Agriculture, Department of Agricultural Structures and Irrigation, 07070 Antalya, Turkey article info Article history: Received 24 October 2011 Received in revised form 12 March 2013 Accepted 15 March 2013 Available online 25 April 2013 Keywords: Greenhouse Heating requirement Heating costs Mediterranean Region Turkey abstract Greenhouse cultivation has a special place in agricultural production. The most distinctive characteristic of the greenhouse cultivation compared to other agricultural production method is that it is carried out under a structure called greenhouse. The air conditioning systems in greenhouse provide a suitable environmental condition for agricultural production. This cultivation method has been widely utilized in many different regions of the world. Southern coast of Turkey is an important greenhouse-growing center in Mediterranean basin. In addition to the traditional greenhouse production, there has been an increase in the number of the modern greenhouse structures that allows climate control in Turkey in recent years. Heating is an important factor in providing favorable climate conditions for greenhouse production that affects directly both quality and cost of the production. Heating of greenhouses is required for an efficient and reliable production especially during winter time in Turkey. Currently, coal is preferred as a fuel in the greenhouse heating because it is more economical in comparison to the other fuels such as diesel, LPG, LNG and natural gas and can be easily supplied. In this study, the heating requirements and their costs for the provinces in the Mediterranean region have been identified by using the meteorological data. The calculations were made for a gothic roofed and coal heated, plastic model greenhouse located in an area with 1 ha representing modern greenhouses of the region. According to the results of calculations, total annual heating requirement was between 3,592,848 and 10,459,688 MJ/ha. The calculated total annual and hourly costs per ha were 65,891.5– 151,220.6 $/year and 23.8–34.2 $/h, respectively. & 2013 Elsevier Ltd. All rights reserved. Contents 1. Introduction ........................................................................................................ 483 2. Materials and methods ............................................................................................... 485 2.1. Research region ............................................................................................... 485 2.2. A model greenhouse ........................................................................................... 485 2.3. Calculations .................................................................................................. 485 3. Results and discussion................................................................................................ 487 3.1. Heating requirement ........................................................................................... 487 3.2. Heating costs ................................................................................................. 488 4. Conclusion ......................................................................................................... 489 Acknowledgment ....................................................................................................... 489 References ............................................................................................................. 489 1. Introduction As a result of misused agricultural land, rapid population growth and inadequate product quality, precautions that will help to increase the productivity must be taken as soon as possible. These precautions include providing and distributing the inputs Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/rser Renewable and Sustainable Energy Reviews 1364-0321/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.rser.2013.03.026 n Corresponding author. Tel.: +90 242 310 2484/+90 242 310 6522; fax: +90 242 227 4564. E-mail addresses: [email protected], muradcanakci@hotmail. com (M. Canakci), [email protected] (N. Yasemin Emekli), [email protected] (S. Bilgin), [email protected] (N. Caglayan). 1 Tel.: +90 242 310 6542; fax: +90 242 227 4564. 2 Tel.: +90 242 310 6506; fax: +90 242 227 4564. 3 Tel.: +90 242 310 6545; fax: +90 242 227 4564. Renewable and Sustainable Energy Reviews 24 (2013) 483–490
Transcript
Renewable and Sustainable Energy Reviews 24 (2013) 483–490
Contents lists available at SciVerse ScienceDirect
Renewable and Sustainable Energy Reviews
1364-03http://d
n Corrfax: +90
E-mcom (Msbilgin@
1 Te2 Te3 Te
journal homepage: www.elsevier.com/locate/rser
Heating requirement and its costs in greenhouse structures: A case studyfor Mediterranean region of Turkey
Murad Canakci a,n, N. Yasemin Emekli b,1, Sefai Bilgin a,2, Nuri Caglayan a,3
a Akdeniz University, Faculty of Agriculture, Department of Agricultural Machinery, 07070 Antalya, Turkeyb Akdeniz University, Faculty of Agriculture, Department of Agricultural Structures and Irrigation, 07070 Antalya, Turkey
a r t i c l e i n f o
Article history:Received 24 October 2011Received in revised form12 March 2013Accepted 15 March 2013Available online 25 April 2013
Greenhouse cultivation has a special place in agricultural production. The most distinctive characteristic ofthe greenhouse cultivation compared to other agricultural production method is that it is carried out under astructure called greenhouse. The air conditioning systems in greenhouse provide a suitable environmentalcondition for agricultural production. This cultivation method has been widely utilized in many differentregions of the world. Southern coast of Turkey is an important greenhouse-growing center in Mediterraneanbasin. In addition to the traditional greenhouse production, there has been an increase in the number of themodern greenhouse structures that allows climate control in Turkey in recent years. Heating is an importantfactor in providing favorable climate conditions for greenhouse production that affects directly both qualityand cost of the production. Heating of greenhouses is required for an efficient and reliable productionespecially during winter time in Turkey. Currently, coal is preferred as a fuel in the greenhouse heatingbecause it is more economical in comparison to the other fuels such as diesel, LPG, LNG and natural gas andcan be easily supplied. In this study, the heating requirements and their costs for the provinces in theMediterranean region have been identified by using the meteorological data. The calculations were made fora gothic roofed and coal heated, plastic model greenhouse located in an area with 1 ha representing moderngreenhouses of the region. According to the results of calculations, total annual heating requirement wasbetween 3,592,848 and 10,459,688 MJ/ha. The calculated total annual and hourly costs per ha were 65,891.5–151,220.6 $/year and 23.8–34.2 $/h, respectively.
As a result of misused agricultural land, rapid populationgrowth and inadequate product quality, precautions that will helpto increase the productivity must be taken as soon as possible.These precautions include providing and distributing the inputs
Q Total heat power (Heating requirements)QK Amount of heat loss from the greenhouseQG Amount of incoming solar radiation inside the
greenhouseIo Average daily solar radiation intensityAr Roof areaηs Conversion ratio of solar energy to beneficial energy
for greenhouse heating during the day.ΣAo Total area of the coverU Overall heat transfer coefficientti Greenhouse inside temperatureto Greenhouse outside temperatureΣQm Monthly heating requirementHHd Daily heating hour
DNm Number of day per monthL Total length of pipeQh Maximum heating requirement in greenhoused Pipe diameterUp Heat transfer coefficient of the pipetp Average of the temperatures of the water exiting from
and returning the furnaceCA Annual fixed costCo Construction cost of heating systemi Real interest raten Heating system’s lifeCRm Monthly coal requirementLHV Low heat energy value of coalη Efficiency of the heating systemCCm Coal cost per monthCP Coal price
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required for use of modern technology in agricultural production,advancing vegetable, fruit production and especially extendinggreenhouse areas [1]. Over the last two decades, use of solaragricultural greenhouses in agricultural production has increased.The primary objective of a greenhouse is to produce higher yieldduring the non-cultivation season, which is possible by maintain-ing the optimum temperature at every stage of the crop [2,3].An appropriate air conditioning including heating or cooling canbe coupled with the greenhouse for this purpose. These, as aresult, will have significant impacts on the cultivation time, qualityand quantity of the products [2].
A greenhouse can be defined as a sophisticated structure,providing ideal conditions for satisfactory plant growth andproduction throughout the year. The inside environment of thegreenhouse is controlled by growth factors including light, tem-perature, humidity and air composition. These are scientificallycontrolled to provide the optimum level throughout the cultiva-tion period, thus increasing the productivity several folds [4].
The greenhouse climate with the optimum value in terms oflight, temperature, ventilation and moisture directly affects thesuccess of the production. Among these factors, the temperature isone of the most important climatologic factor should be createdinside the greenhouse [5]. The vital (physiological and biological)activities of the plants usually slows down at +7 1C, and ceases at0 1C [6]. Providing appropriate temperature and humidity in thegreenhouse help to decrease diseases and usage of pesticides.Thus, problem of pesticide residue on crops is alleviated and highquality of products is obtained. It is reported that 10 1C increase ingreenhouse temperature provides two-fold increase in yield.In addition, heating operations shortens the growth period andreduces labor requirements. Therefore, heating of the greenhousesis necessary at night or even daytime hours in case of insufficientsolar radiation [5,7]. In contrast, heating is one of the mostimportant cost factors in greenhouse cultivation and its profit-ability. Therefore, heating operations carried out for the needs ofplants in some regions might not be economical. In these regions,the operation should be applied only to protect plants from frosthazard.
Greenhouse cultivation has a widespread area in the world.For greenhouse cultivation, countries can be classified as the coolclimate zone (Holland, England, Germany, etc.), the temperateclimate zone (Mediterranean coastline, Spain, Italy, Turkey, Greece,Israel, Egypt etc.) and the zone where the countries are dominatedby two climate zones (USA, Japan etc.) by considering theirlatitude and greenhouse technologies. It is stated that greenhousecultivation is more favorable in the countries located between 30
and 40 degrees of latitude. The cooling costs increase below 30th,while heating costs above the 40th degree of latitude [8].
A greenhouse air conditioning system is used to increase thethermal energy storage inside during the day or to transfer excessheat from inside the greenhouse to the heat storage area [9].Heating is required for the greenhouses in the Northern Europeancountries in the cool climate zone. In many Mediterraneancountries, even in cold nights heating is not realized. This situationleads to low quality and efficiency in products. To heat thegreenhouses, instead of fossil fuels alternative energy sourcesand energy conservation should be taken into consideration.Solar energy is an important alternative energy source and is asignificant opportunity for the Mediterranean basin and the Arabcountries zone. In spite of being a cheap and favorable source,solar energy has some economic and technical drawbacks [10].Therefore, many researches have been conducted related to heat-ing of greenhouse with alternative energy resources.
A study was carried out to store solar energy in an under-ground rock-bed for greenhouse heating. The results showed thatthe rock-bed system created an air temperature difference of about10 1C at night. Furthermore, it kept the inside air temperaturehigher than that of outside air at night, even in an overcast dayfollowing a clear day [11]. Kasap and Erdem (1994) realized a studyto compare different heating systems with a geothermal one inTokat Province, Turkey. It was concluded that the heating systempowered by geothermal energy was more economical in bothglass- and plastic-houses [12]. Bascetincelik and Ozturk (2003)investigated energy and exergy efficiency of a packed-bed heatstorage unit for greenhouse heating. In the study, solar energy wasstored daily using the volcanic material with the sensible heattechnique for heating the tunnel greenhouse of 120 m2. The resultsshowed that 18.9% of the total heating requirement of the tunnelgreenhouse was obtained from the heat storage unit [13]. Lazâar etal., [14] compared economy of a solar system for greenhouseconditioning in order to maintain the greenhouse air temperatureat 12 1C at night during the coldest months with a conventionalheating system, concluded that greenhouse heating by a solarsystem was environmentally-friendly and more profitable but lesspowerful than a conventional system [14].
Bargach et al. [15] realized an experimental investigation byusing two different types of solar systems to reduce heating costsin traditional greenhouses in Morocco [15]. Karacabey [16] pro-founded necessary information for the growers about the cost ofheating that significantly affects the production costs of green-houses. For this purpose, fixed and variable costs for heating byeither brown coal or geothermal hot water for a typical
Table 1Protected cultivation area in the Mediterranean Coastline of Turkey [18].
Province Glasshouse Plastichouse High tunnel Low tunnel Total area
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greenhouse operation located in Balçova district of Turkey werecalculated. It has been found that fixed costs of brown coal were27% bigger than geothermal hot watery heating systems. In pointof variable operation costs, brown coal had nearly ten-fold costless than geothermal hot watery heating systems [16].
Located in the Mediterranean countries zone, Turkey is aprominent center of greenhouse cultivation. Today, the annualexport value of greenhouse vegetables has reached 453 million $[17]. Greenhouse cultivation began in the 1940s and the amount ofgreenhouse areas increased with the start of plastic use as thecovering material after the 1970s. Total protected cultivation areaof Turkey is 59,961 ha of which 31,673 ha (52.8%) is greenhouse[18]. Vegetables (95%) are the primary production type in thegreenhouse areas where ornamental plants and seedlings are alsogrown. Greenhouse vegetable growing in the region is performedwidely in the farmer greenhouses by traditional methods. Theheating operation is done only to protect plants from frost hazardsand the traditional wood stoves are used fuel for this purpose [19].However, inadequate levels of the heating process affect theproduction quality and the yield negatively, and cause the diseasesto multiply. On the other hand, changes in consumer demand andenvironmentally conscious manufacturing have brought up foodproduction techniques highlighting the food security and relatedcertification processes (Good Agricultural Practice—GAP). There-fore, after the 2000s, climate-controlled modern greenhouseapplications obtaining higher quality products and food securityhas been widespread applications [20,21]. Modernization for thegreenhouses can be defined as the usage of relatively hightechnologies on the subjects of structure–cover material, airconditioning systems and cultivation techniques. These green-houses are located mostly in the Mediterranean region. Themodern greenhouses with high initial investment costs haveautomation systems to maintain climate control soilless culture.Total investment cost (except land price) of a modern plasticgreenhouse with 30 ha was indicated as 604,500 $/ha [20].
The modern greenhouses in the research area have hot waterpiped heating systems. Currently, coal is preferred as a fuel in thegreenhouse heating because it is more economical in comparisonto the other fuels such as diesel, LPG, LNG and natural gas and canbe easily supplied. Today, the total area of modern greenhouses inTurkey is 300 ha and 92% of which used for tomato and peppercultivation [18]. Thanks to favorable regional climate and aneconomical type of production opportunity, the number hasincreased in recent years. Heating costs are one of the importantexpenses in this type greenhouse cultivation. Therefore, heating-related calculations should be done carefully in managementstudies carried out for economical production.
In this research, the heating requirements and costs for a modelmodern plastic greenhouse were determined by considering themeteorological data for five provinces located in the Mediterra-nean region in Turkey.
2. Materials and methods
2.1. Research region
Turkey's southern coast covering Muğla, Antalya, Mersin, Adanaand Hatay provinces are located on the east of Mediterranean Sea.Agricultural production is carried out in very different productionbranches thanks to favorable geographical and climatic features inthe region. Geographic location of the research area is shown inFig. 1.
Protected cultivation areas of the selected provinces and also ofTurkey's total are given in Table 1. The glasshouses and plasticgreenhouses in the region constitute about 99.0% and 91.4% of theof Turkey's total glasshouses and plastichouse areas (Table 1).In the selected regions, greenhouse farming generally starts in themonths of August or September depends on the crop and themethod of growing and continues until the end of June. Somelong-term meteorological data of each province are presented inTable 2, Figs. 2 and 3 [22].
2.2. A model greenhouse
In this study, considering the conditions of the region and farmproperties a typical plastic greenhouse has been identified as amodel (Fig. 4) and used as material. The model greenhouse hasgothic roof and 10 tunnels with a total width of 96.0 m, length of104.2 m floor area of 10,003 m2, cover surface area of 13,055 m2,side wall height of 4.5 m and ridge height of 6.5 m. Its coveringmaterial is single-layer plastic.
2.3. Calculations
Appropriate heater capacity, monthly heating requirementsand the operating costs for heating operations of the modelgreenhouse were calculated in this study. The desired amount ofheat power (heating requirement) to ensure the ambient insidetemperature of the greenhouse was calculated by using Eq. (1):
Q ¼ QK−QG ð1Þwhere, Q is the total heat power (W), QK is the amount of heat lossfrom the greenhouse, (W), QG is the amount of incoming solarradiation inside the greenhouse (W).
The amount of incoming solar radiation can be determinedfrom Eq. (2):
QG ¼ Io � Ar � ηs ð2Þ
where, Io is the average daily solar radiation intensity (W/m2), Ar isthe roof area (m2), ηs is the conversion ratio of solar energy tobeneficial energy for greenhouse heating during the day (decimal)and this value is accepted as 0.5 [5,16].
Fig. 1. Locations of the study areas.
Table 2Some meteorological data of the selected provinces [22].
Fig. 2. Mean temperature values for the selected provinces.
0
5
10
15
20
25
30
I II III IV V VI VII VIII IX X XI XII
Sola
r rad
iatio
n M
J/m
2 da
y
Months
Antalya Muğla Mersin Adana Hatay
Fig. 3. Solar radiation values for the selected provinces.
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The amount of heat loss from the greenhouse can be deter-mined by using Eq. (3) [5,7,8].
QK ¼ ΣAo � U � ðti−toÞ ð3Þ
where, ΣAo is the total area of the cover (m2), U is overall heattransfer coefficient (W/m2 K), ti and to are greenhouse inside andoutside temperatures (1C), respectively.
In this study, monthly heating requirement value (MJ/ha) wasdetermined by take into consideration the values of heat loss (QK).The value was calculated by using Eq. (4) [7]. Also, the annualheating requirement of the greenhouses can be found by collecting
of the monthly values.
ΣQm ¼ ΣAo � U � ðti−toÞ � 3:6� HHd � DNm ð4Þwhere, ΣQm is monthly heating requirement (kJ), HHd is dailyheating hour (h/day) and DNm is number of day per month (day/month).
For the selected provisions, the average values of temperature,solar radiation intensity and sun exposure duration were obtainedfrom the long-term records of the State Meteorology AffairsGeneral Directorate and used in the calculations [22].
The total value related to coefficient of heat transfer in thegreenhouse (U) depends on various factors such as the size of thegreenhouse, type of the cover material and heaters, wind speedetc. Therefore, it is reported that complete and accurate determi-nation of heat transfer coefficient is not possible, so, the coefficientvalues determined and proposed based on experience rather thandetailed calculations were used for the application processes.In the calculations, a value of 6.8 W/m2 K can be used as totalheat transfer coefficient [5,23–25]. Since mostly vegetables aregrown in the region greenhouses, the required inside tempera-tures at night and daytime were considered as 16 and 21 1C,respectively [5,23,24,26]. Considering the calculations, it has beenidentified that heating is not necessary during the daytime since
Fig. 4. View and dimensions of the model greenhouse.
0
5
10
15
20
25
30
I II III IV V VI VII VIII IX X XI XII
Ave
rage
nig
ht te
mpe
ratu
re,°C
Months
Antalya Muğla Mersin Adana Hatay ti
Fig. 5. Average night temperature values for the selected provinces.
Table 3The average monthly heating time (h/month) for the selected provinces.
M. Canakci et al. / Renewable and Sustainable Energy Reviews 24 (2013) 483–490 487
the average solar radiation meets the heat loss of the greenhouse.Therefore, heating calculations were done for the night time inwhich there is no solar radiation. It was stated that lowertemperatures of the region must be considered instead of averageminimum temperatures to determine the heater capacity. There-fore, as a minimum outside temperature value, 3 1C for Antalyaand Mersin, 0 1C for Adana and Hatay provinces and −3 1C forMuğla province was used in the heater capacity calculations [7,8].Eq. (5) was used to calculate the total pipe length for the heatingsystem [5,16]:
L¼ Qh
½π � d� Up � ðtp−tiÞ�ð5Þ
where, L is the total length of pipe (m), Qh is the maximum heatingrequirement in greenhouse (W), d is the pipe diameter (m), Up isheat transfer coefficient of the pipe (W/m2 K), tp is the average ofthe temperatures of the water exiting from and returning thefurnace (1C). The heating pipe diameter and pipe heat transfercoefficient were regarded 51 mm and 13 W/m2 K, respectively[5,8]. It was also considered that temperature of the water comingout of the furnace was 80 and that of returning water was 60 1C inthe calculations.
Fixed and variable costs were taken into account in determin-ing the costs of the heating system. Fixed costs can be calculatedby using Eq. (6) [16,27]. The equation includes expenses ofdepreciation and interest:
CA ¼ Co � ði� ð1þ iÞnÞðð1þ iÞn−1Þ
� �ð6Þ
where, CA is the annual fixed cost ($/year), Co is the constructioncost of heating system ($), i is the real interest rate (decimal), n isthe heating system's life, year. Real interest rate was taken as 0.08in terms of 2009 in Turkey [28]. The life of heating systems wasassumed as 20 years [16].
Basic variable costs of heating system consist of fuel, labor, andelectricity and maintenance inputs. The labor and electricity costswere determined by consulting heater manufacturers and
greenhouse farmers. A general approach, the system maintenancecosts were regarded as 5% of the investment cost [16].
Fuel requirement per month was calculated by using thefollowing Equation [23]:
CRm ¼ ΣQm
ðLHV � ηÞ ð7Þ
where, CRm is the monthly coal requirement (kg), LHV is the lowheat energy value of coal (kj/kg), η is the efficiency of the heatingsystem. In the calculations, the low heat energy value of coal andefficiency value for the heating system were considered as28010 kj/kg and 80%, respectively [29]. In addition, $250/ton asthe coal price was considered in fuel costs calculations givenbelow:
CCm ¼ CP � CRm ð8Þwhere, CCm is the coal cost per month ($/h), CP is the coal price($/kg),
3. Results and discussion
3.1. Heating requirement
Average annual night temperature values of the selectedprovinces were given in Fig. 5. As seen in this figure, heatingoperations should be realized for section below the straight line of16 1C which is accepted as the favorable inside temperature (ti) ingreenhouse vegetable growing. For this reason, heating operationneeds to be realized in the period between November and April inthe provinces of Antalya, Adana and Hatay, October and May inMuğla and October and March in Mersin province. The periodrequired for the heating operation depends on both the tempera-ture and the length of the solar radiation time. Total monthlyheating time (hour) and heating requirements (MJ/ha) calculatedfor the specified period of each province are presented inTables 3 and 4. According to Table 3, the shortest heating periodis required for Mersin (2764.5 h/year) and the longest for Muğlaprovince (4424.4 h/year). Muğla province has the lowest nighttemperature values and needs heating operations two or threemonths more than the others. January was determined as the
M. Canakci et al. / Renewable and Sustainable Energy Reviews 24 (2013) 483–490488
month in which the heating requirement is the highest (Table 4).This value ranged from 1,198,372–2,236,248 MJ/ha for the pro-vinces. Muğla province has the highest annual heating require-ment (10,459,688 MJ/ha) whereas Mersin has the lowest(3,592,848 MJ/ha). High average temperature values and long solarradiation time caused lower values in Mersin province.
3.2. Heating costs
Fuel consumption is one of the most important factors amongall cost inputs in greenhouse operations. In the research area, coalis used widely as fuel due to low price. It can be said thatgreenhouse farmers prefer imported coal because of its highcalorific value, but some farmers prefer local lignite coal. Thecalculated findings related to coal requirements and costs for theprovinces are given in Table 5. As shown in Table 5, annual coalrequirement ranged between 160.34 and 466.78 t/ha dependingon the heating requirements and heating time. Muğla has thehighest coal costs in respect to coal prices (108,916 $/ha). Hatay(59,952 $/ha), Adana (58,544 $/ha), Antalya (55,150 $/ha) andMersin (37412 $/ha) provinces are followed by Muğla Province.
Heating systems with solid fuel produced in Turkey are widelyused in greenhouses. After the 2000s, with the increases inmodern greenhouse areas, some local firms producing heatersfor different purposes have begun to produce heating systems forgreenhouses. The heater capacity values, total pipe lengths and thesystem's fixed costs for each selected provinces were calculated inthe scope of the study and are presented in Table 6. Total heatingrequirement values of the model greenhouse changed from 4155–6072 MJ/h per ha, and total length of steel pipe values rangedbetween 10266 and 15004 m. Also, the heater capacities requiredfor the model greenhouses were between 5193 and 7590 MJ/h.
Prices of the other system components include circulationpumps, fittings, valves, stopcocks, control systems, labor, etc.It was found that heater, hot water pipes and other costs ofthe system together with the construction costs ranged from
Table 4The values of the heating requirement (MJ/ha per month) for selected theprovinces.
101,375–140,677 $ and it was observed that the annual fixed costsof the system are between 10,325 and 14,328 $/ha-year.
Variable costs depending on the use of the system consist ofcoal, labor, electricity and maintenance costs (Table 7). Circulationpumps are used to supply water circulation within the system andelectric motors are used to activate the coal feeding mechanismsand fans in the heaters. The hourly variable cost was ranged from20.1–30.9 $/h per ha. The lowest variable cost value was deter-mined in Mersin and the highest value in Muğla province. Hourlycoal costs have the highest percentage (67–80%) among thevariable cost items. Considering annual usage time of heatingsystems, total annual variable cost values were between 55,566and 136,892 $/year per ha. The annual fixed and the variable costswere considered together and the total annual cost per ha wasgiven in Table 8. The lowest and the highest total cost values perha ranged between 65,891.5 $/year, 23.8 $/h and 151,220.6 $/year,34.2 $/h, respectively.
During the cultivation season, it is important to keep insidetemperature of the greenhouse at favorable value. Sometimes, thegrower can keep inside temperature higher than 16 1C. For all that,it may be required to keep this temperature at lower values than16 1C for some period due to economic reasons. Because, theharvested crop price may fall or fuel price may increase duringthe growing season. The values showing the change in the totalvariable costs were given Fig. 6. There is a linear relationshipbetween inside temperature in the greenhouse and the totalvariable costs and R2 values in the regression equations are over0.99. If Fig. 6 is investigated, it can be seen that 1 1C variation onheating operations causes important changes in variable costs.These variations are so important in terms of economic productionand profitability. Some different precautions can be considered todecrease variable costs like usage of double plastic cover andthermal screen in the greenhouses. The protection methodsdecrease heat transfer coefficient and heating requirement espe-cially at nights. Thus, it can be seen that some greenhouse farmersbegun to use thermal screen.
Alternative energy sources can be used in terms of botheconomy and the environment. It is a well-known fact today thatdue to decline of the world's fossil energy resources and theenvironmental impacts of the resources, utilization and storage ofrenewable energies are by no means, issues which should beneglected [11]. It can be seen that solar and geothermal energyresources are applied in some regions in Turkey. It can be said that,the selected regions have not sufficient geothermal energyresources but an important potential concerning solar energy.Solar energy as an abundant but not used yet, clean and safesource, is an attractive substitute for conventional fuels for passiveand active heating of greenhouses. It was shown that, solar energycan be stored in an underground rock-bed and used on green-house heating operations economically [11]. In the region, thegreenhouse farmer should be encouraged and supported for using
Muğla, y = 21157x -111117, R² = 0,9973Mersin, y = 13843x -122230, R² = 0,9915 Adana, y = 15752x -125122, R² = 0,9949
Hatay, y = 16534x -121701, R² = 0,9974Muğla, y = 21157x -111117, R² = 0,9973Mersin, y = 13843x -122230, R² = 0,9915 Adana, y = 15752x -125122, R² = 0,9949
Hatay, y = 16534x -121701, R² = 0,9974Muğla
Antalya, y = 16335x -129580, R² = 0,995
Muğla, y = 21157x -111117, R² = 0,9973Mersin, y = 13843x -122230, R² = 0,9915 Adana, y = 15752x -125122, R² = 0,9949
Hatay, y = 16534x -121701, R² = 0,9974
0
40000
80000
120000
160000
200000
9 10 11 12 13 14 15 16 17 18
Tota
l var
iabl
e co
st, $
/ha-
year
Greenhouse inside temperature,°C
Antalya
MersinAdanaHatay
Fig. 6. Changes in total variable costs related to greenhouse inside temperature.
M. Canakci et al. / Renewable and Sustainable Energy Reviews 24 (2013) 483–490 489
of solar energy systems in heating operation for less fossil fuelconsumption and environmentally-friendly cultivation.
4. Conclusion
Modern greenhouse production areas have continued to rise inTurkey in recent years. Unlike the traditional greenhouses, thesetypes of greenhouses are used for soilless growing and haveautomation systems. Heating process is carried out in accordancewith the plant needs. The heating requirements and costswere calculated for a model greenhouse having an area of
approximately 1 ha at five different provinces. The greenhouseshave central heating systems with hot water and coal is preferredas fuel.
Generally heating is not carried out in the daytime hours due tosufficient intensity of solar radiation. The maximum heatingrequirement was calculated for January at all provinces. Theannual heating requirement ranged between 35,928,487 and10,459,688 MJ/ha. The annual total coal requirement was rangedfrom 160.34–466.78 t/ha, while coal costs were between 37,412and 108,916 $/ha. Total annual fixed cost per ha was rangedbetween 10,325 and 14,328 $/year while the total variable costwas varied from 20.1–30.9 $/h. The calculated total annual andhourly costs per ha were 65,891.5–151,220.6 $/year and 23.8–34.2$/h, respectively.
Considering the climate data, high cost of heating is observedwhen the heating is applied. However, an economical productionis provided thanks to the fact that the purchase prices of theproducts are sufficient and the products can have a place in foreignmarkets in winter season. Moreover, measures including heatconservation in the greenhouses can be taken to reduce heatingrequirements and lower costs. Using thermal screens, double-storied or different types of cover materials and passive solarheating systems will decrease heating requirements in the green-houses. In addition, structural and economic conditions of thebusiness should be assessed and the most suitable method ofheating should be identified.
Acknowledgment
This research was partly supported by Research Fund ofAkdeniz University.
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